stratigraphy n.

"horizontal layer," 1590s, from Modern Latin special use of Latin stratum "thing spread out, coverlet, bedspread, horse-blanket; pavement," noun uses of neuter of stratus "prostrate, prone," past participle of sternere "to spread out, lay down, stretch out," from nasalized form of PIE root *stere- "to spread."

word-forming element meaning "process of writing or recording" or "a writing, recording, or description" (in modern use especially in forming names of descriptive sciences), from French or German -graphie, from Greek -graphia "description of," used in abstract nouns from graphein "write, express by written characters," earlier "to draw, represent by lines drawn," originally "to scrape, scratch" (on clay tablets with a stylus), from PIE root *gerbh- "to scratch, carve" (see carve).